1. Field of the Invention
Embodiments of the present invention relate to a bending-type polymer actuator.
2. Description of the Related Art
In recent years, actuators have been developed. In particular, actuators using polymer materials have been developed. For example, it is known that an actuator having a three-layer structure in which electrode layers are arranged on a front surface and a back surface a plate-like electrolyte layer. This type of actuator is referred to as a bending-type actuator because it bends by applying a voltage between the electrodes.
Japanese Patent Laid-Open No. 2007-028749 discloses an actuator element in which adjacent bending portions bend in mutually opposite directions. This patent literature states that bending motions of the actuator elements are easily converted into linear motions by connecting a plurality of the actuator elements.
FIGS. 4A to 4D illustrate the actuator element 50 described in Japanese Patent Laid-Open No. 2007-028749. FIG. 4A is a perspective view of the actuator element. FIGS. 4B to 4D are explanatory drawings. FIG. 4B illustrates the structure of the actuator element when viewed from the front. FIG. 4C illustrates the structure of the actuator element when viewed from the side. FIG. 4D illustrates the structure of the actuator element when viewed from the rear.
An electrode layer 41a and an electrode layer 42a′ are arranged on the same surface of an electrolyte layer 40. An electrode layer 41a′ and an electrode layer 42a are arranged on a surface (rear surface) opposite the surface on which the electrode layer 41a and the electrode layer 42a′ are arranged. The electrode layer 41a and the electrode layer 42a′ are insulated by an insulating portion 43. The electrode layer 41a′ and the electrode layer 42a are also insulated by the insulating portion 43.
The electrode layer 41a′ is not arranged at a position directly opposite to the electrode layer 41a but is arranged at an offset position. The electrode layer 41a′ is connected to the electrode layer 41a by a narrow electrode portion (connection portion) 44 on a side of the electrolyte layer 40. The electrode layer 42a′ is also arranged at an offset position on the rear surface with respect to the electrode layer 42a. The electrode layer 42a′ is connected to the electrode layer 42a by a narrow electrode portion 45.
The electrode layers 41a and 41a′ have the same potential because they are connected by the narrow electrode portion 44. The electrode layer 42a and the electrode layer 42a′ have the same potential because they are connected by the narrow electrode portion 45.
By applying a voltage difference between opposite electrodes, one half of the actuator element 50 undergoes bending deformation so as to have a convex shape, the other half undergoes bending deformation so as to have a concave shape.
The actuator element possesses the following problems.
(1) The electrode layers on the front and rear surfaces are connected by the narrow electrode portions on the sides of the actuator element. So, electric fields at electrode portions are disturbed, causing nonuniform bending deformation or twisting. As a result, local stresses occur near the narrow electrode portions, causing the detachment of the narrow electrode portions, in some cases.
(2) Because the narrow electrode portions are used, the portions are broken by an external force.